Molecular phylogeny and taxonomic revision of chaetophoralean ...

7. Conclusions of the thesis
In the present contribution, the first detailed molecular phylogenetic investigation of the
order Chaetophorales s.s. based on the nuclear-encoded SSU rRNA gene has been
provided. Moreover, it has been clearly demonstrated that the traditional delimitation of
the common chaetophoralean genera (Chaetophora and Stigeoclonium) based
exclusively on structural characters is inconsistent with the results obtained by the 18S
rDNA phylogeny. The revealed polyphyly of the genera Chaetophora and
Stigeoclonium has been further supported by NHS molecular synapomorphies in the
SSU rRNA secondary structure. Although the nuclear-encoded SSU rRNA gene has
proven to be insufficient to unravel all phylogenetic relationships, the results gained
obviously indicate either a homoplasious or plesiomorphic trait of some commonly used
taxonomic features, and call for an overhaul of the systematics of the Chaetophorales
using new morphological and molecular approaches. In addition, a first detailed
comparative investigation of the ITS2 secondary structure as well as tracing the
evolutionary history of all ITS2 substitutions in the green algal order Ulvales led to a
completely new view into ITS2 evolution demonstrating the weakness of the generally
accepted rules delineating the CBC ITS2-clade species concept. It came as surprise that
most CBC-clades sensu Coleman are not monophyletic, and that at least in the Ulvales,
the presence of CBCs is not restricted to a single taxonomic level. Beside that it has
been clearly shown that the simple comparison of ITS2 characters among pairs of taxa
without consideration of their evolutionary history (i.e. phenetic approach) can be
misleading. Therefore a generally applicable suite of methods providing a detailed view
into ITS2 by directly tracing the evolution of individual characters has been proposed.
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